1. Field of the Invention
The present invention relates to a technique for encrypting and decrypting video data.
2. Description of the Related Art
Techniques are available to encrypt or scramble video data to control accessibility to the video data. In accordance with such a technique, the video data is encrypted using encryption key information, and only users who have decryption key information corresponding to the encryption key information are able to correctly replay the video data.
Since the amount of information of video data is typically large, compression encoding is typically used. For example, Standard JPEG2000, standardized by ISO/IEC JTC 1/SC 29/WG1, is typically used as a compression technique. Encryption may be applied to video data that has been compressed using the JPEG2000 Standard. The video data is thus efficiently transferred and stored, and access to the video data is also controlled.
Using a compression technique such as JPEG2000, the video data is compressed in a hierarchical structure in terms of resolution, video quality, spatial domain, and components forming pixels. If the video data is encrypted in accordance with the hierarchical structure, access control may be performed taking into consideration the hierarchical structure.
If access control is performed on a per resolution basis so that a high-resolution component can only be encrypted with a low-resolution component left unencrypted, any user can replay the low-resolution video data. The high-resolution component can only be correctly replayed by a user who is permitted to use a decryption key (the owner of a decryption key).
Encryption in an encoding (compression) domain is possible when video data such as the one compressed in accordance with the JPEG2000 Standard is encrypted.
In accordance with one of those techniques, an encryption process is performed on a coefficient of video data subsequent to quantization in a JPEG2000 compression process (or code bit plane of the coefficient), and the encrypted quantization coefficient is entropy encoded. Encrypted compressed data thus results (a first encryption method). This encryption method allows the encryption process to be performed in the middle of the compression process if the video data needs to be compressed and encrypted. The first encryption method reduces the entire process time, thereby efficiently encrypting the video data. The video data that has been encrypted using the first encryption method is compatible with the JPEG2000 Standard.
In accordance with another technique, an encryption process is performed on video data that is at a final stage of a compression process in accordance with the JPEG2000 Standard. Encrypted video data thus results (a second encryption method). The second encryption method achieves an efficient encryption, requiring a short process time for the encryption process when the already compressed data is subjected to the encryption process. The second encryption method has an advantage that the compressed data remains unchanged in the amount of data after the encryption process.
It is also contemplated that video data is encrypted in a different encoding (compression) domain.
Data can be encrypted in a variety of encoding domains. The encrypted data can then be decrypted. However, when the data is decrypted, it becomes difficult to identify the domain from which the data was encrypted which makes the decryption of the data difficult.
In the above-mentioned encryption techniques, video data is encrypted in a predetermined compression domain. However, it is difficult to set a plurality of compression domains, and to encrypt video data in one compression domain selected from the plurality of compression domains. It is also difficult to simultaneously use the first and second encryption methods.